The standard addition method revisited

Several flaws of the conventional standard-addition method (SAM) have been unravelled. By revisiting the theory, it has been shown that the SAM cannot be used to correct completely for interferences in analytical chemistry. Therefore, a new theory of SAM was developed, which takes into account the uncertainty of measurement and relates this information to differences that might stem from interferences. The SAM may be used to correct for rotational effects but it cannot be used to correct for translational effects, which confirms earlier findings. A full set of equations were supplied for undertaking a full method validation including a new set of parameters of performance. The equations were tested on determination by UV–VIS spectrophotometry of L-ascorbic acid. Previous results are reviewed and discussed in view of these new findings and recommendations are given about the importance of carrying out full method validations as a prerequisite to the SAM.